Venturi scrubbers use turbulence (a venturi) and an absorbing liquid to create a pressure drop between the front and back of the scrubber.  The pressure drop from the contraction creates thorough mixing of the liquid being fed into the scrubber at the throat and the gas moving through the scrubber.

The scrubbers are used to take out particulate and to remove gas.  In removing CO2, and HCl and some SO2/SO3 from stack gasses, as well as particulate, the scrubbers use an alkaline solution usually with either soda ash or with caustic soda.  The gasses react with the alkaline liquid and the byproducts are solubilized in water. In some instances a lime/ water solution is used in the scrubber but it has very high maintenance due to lime fouling.

As you might imagine, the scrubber entrains a lot of water, and it is usually followed by a chevron type de-mister to remove the water vapor.  At that point, the gas is most often saturated, and the water collected from the scrubber throat and from the demister contain most of the reacted products and the particulates from the scrubber. Scrubbers are up to 100% effective in removing certain types of acid gasses, and depending upon pressure loss, between 75 and 95% effective in removing particulates from stack gasses.  The particulates remaining in the gas flow are generally very fine and respirable.

A good reference source for basic scrubber information is http://www.ceilcoteapc.com/pr_venturi_type.htm#fixed